Salmonella and Colitis in Horses

Affected horses often need intravenous fluids to combat diarrhea, one of the most common clinical signs of both salmonellosis and colitis.

Photo: Anne M. Eberhardt/The Horse

Salmonellosis and colitis--two equine ailments that are commonly associated with each other--are a bit like the chicken and the egg: you don't always know which came first, said Jamie DeFazio, CVT, VTS-EVN, nursing supervisor at the University of Pennsylvania School of Veterinary Medicine's New Bolton Center, in Kennett Square.

"Colitis (inflammation of the large or small colon) can either develop as a result of salmonellosis, or can be the primary condition that predisposes the horse to salmonellosis," she said during a presentation at the American Veterinary Medical Association Convention, held July 16-19 in St. Louis, Mo.

Although the two ailments commonly occur in tandem (especially in clinical settings, DeFazio noted), they are in fact two different problems that can arise independently as well.

Colitis

Colitis can be a dangerous ailment for affected horses: "With any inflammation or irritation of the gut, the natural flora is disrupted and can lead to diarrhea (and) proliferation of harmful bacteria," said DeFazio. "In some cases the colon can be so badly insulted that surgery is necessary to remove a portion of the colon (usually due to right dorsal colitis). In some cases the colon may not regain proper functionality, leading to the demise of the animal."

Common causes of colitis, according to DeFazio, include some antibiotic treatments, heavy doses of non-steroidal anti-inflammatory drugs over an extended period of time, parasites, and bacteria.

Salmonella

Salmonella spp. cause a multitude of problems in horses, including diarrhea, abscesses, septicemia, and other ailments. Clinical signs of salmonellosis include anorexia, fever, lethargy, and diarrhea. Salmonellosis usually manifests as colitis and diarrhea.

Horses can contract salmonella by ingesting contaminated food or water. In some cases, lax husbandry practices (such as using a common feed tub for several horses without disinfecting it between uses, or interacting with several horses without washing your hands) can cause the Salmonella bacteria to spread via equipment or people's hands. Rodents and birds can also spread the disease. Thus, it is important to clean and disinfect contaminated areas and equipment regularly.

"Good biosecurity practices are crucial in limiting the spread of this contagious infectious disease (salmonella), as it is not only highly transmissible to other horses, it is also zoonotic," DeFazio said. If you suspect a horse has salmonellosis and/or colitis, isolate him and practice good biosecurity to prevent spreading infection to other horses or people.

Many healthy horses carry small amounts of Salmonella in their gut. The bacteria usually do not cause a problem, however, because "good" bacteria keep them in check. About 1-2% of horses shed the bacteria in their manure without being sick, which could make preventing the spread of Salmonella difficult without good biosecurity practices in place. If the horse does develop colitis, the inflammation can cause Salmonella to multiply, initiating a problem. "You can't necessarily pick these shedder animals out," DeFazio said. "In these animals that do not have any clinical signs, Salmonella is only identified by random culture."

Horses are more likely to shed the bacteria--and thus spread the disease to other horses--if they encounter stressors such as shipping, showing, changes in diet, antimicrobial use, and illness.

Occurring In Tandem

Diarrhea, one of the most common clinical signs of salmonella and colitis infections, can generally be treated with kaolin-pectin, bismuth products, or Biosponge. ("These treatments are to help clear up the diarrhea," DeFazio noted. "Kaolin-pectin and bismuth help to coat and soothe. Biosponge helps to firm up the manure and also binds with endotoxins.") Probiotics might also be helpful as they introduce more "good" bacteria to promote healthy GI function and could lessen the need for antibiotics. Antibiotics might not be the best treatment choice, DeFazio warned, because they could make the problem worse.

"Antibiotics may prolong shedding," she explained. "Antibiotics are not usually used unless there is a concern with systemic disease, which is usually indicated by a fever or low white blood cell count, and antibiotic selection is usually limited."

The horse also might need intravenous (IV) fluids and nutritional support, such as a variety of high quality forage and complete grain feeds, to get on the road to recovery, she noted.

"If the horse is not eating, nasogastric feedings or IV parenteral nutrition may be necessary," she added.

Persistent, untreated diarrhea can quickly lead to dehydration and even death (due to severe dehydration, which can cause serious electrolyte abnormalities that can affect multiple organ systems), DeFazio added, so don't hesitate to call the veterinarian in this situation.

"Salmonella can be a cause of colitis (you don't know until you perform a fecal culture), or salmonella can cause colitis (the proliferation of the bacteria can majorly alter the gastrointestinal flora and lead to colon inflammation)," De Fazio concluded. "Whereas Salmonella or Clostridia are the most common causes of colitis, you can have colitis without initial presence of salmonella (such as from NSAID use), and the salmonella could develop secondary to the colitis.

"You may have a horse with a positive culture for salmonella that developed the colitis from the disruption in gut flora, in which case the colitis was brought on by the salmonella. Sometimes you really don't know what came first."

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